自下而上分析基本问题
规约
我们所讨论的自下而上分析法是一种“移进－归约”法。这种方法的大意是，用一个寄存符号的先进后出栈，把输入符号一个一个地移进到栈里，当栈顶形成某个产生式的一个候选式时，即把栈顶的这一部分替换成（归约为）该产生式的左部符号。
算符优先分析
所谓素短语是指这样的一个短语，它至少含有一个终结符，并且，除它自身之外不再含任何更小的素短语。所谓最左素短语是指处于句型最左边的那个素短语。
代码：
#include <iostream>
#include <cstring>
#include <cstdio>
#include <vector>
#include <stack>
#include <map>
#include <set>
#include <algorithm>
#include <string>
#include <cstdlib>
#include <cctype>
#define MAX 507
using namespace std;
class WF
{
public:
string left;
vector<string> right;
WF ( const string& str )
{
left = str;
}
void insert ( char str[] )
{
right.push_back(str);
}
void print ( )
{
printf ( "%s->%s", left.c_str(), right[0].c_str() );
for ( int i = 1 ; i < right.size() ; i++ )
printf ( "|%s", right[i].c_str() );
puts("");
}
};
char relation[MAX][MAX];
vector<char> VT;
vector<WF> VN_set;
map<string,int> VN_dic;
set<char> first[MAX];
set<char> last[MAX];
int used[MAX];
int vis[MAX];
void dfs ( int x )
{
if ( vis[x] ) return;
vis[x] = 1;
string& left = VN_set[x].left;
for ( int i = 0 ; i < VN_set[x].right.size() ; i++ )
{
string& str = VN_set[x].right[i];
if ( isupper(str[0]) )
{
int y = VN_dic[str.substr(0,1)]-1;
if ( str.length() > 1 && !isupper(str[1] ) )
first[x].insert ( str[1] );
dfs ( y );
set<char>::iterator it = first[y].begin();
for ( ; it!= first[y].end() ; it++ )
first[x].insert ( *it );
}
else
first[x].insert ( str[0] );
}
}
void make_first ( )
{
memset ( vis, 0, sizeof ( vis ) );
for ( int i = 0 ; i < VN_set.size() ; i++ )
if ( vis[i] ) continue;
else dfs ( i );
#define DEBUG
#ifdef DEBUG
puts("------------FIRSTVT集-------------------");
for ( int i = 0 ; i < VN_set.size() ; i++ )
{
printf ( "%s : ", VN_set[i].left.c_str() );
set<char>::iterator it = first[i].begin();
for ( ; it!= first[i].end() ; it++ )
printf ( "%c ", *it );
puts ("" );
}
#endif
}
void dfs1 ( int x )
{
if ( vis[x] ) return;
vis[x] = 1;
string& left = VN_set[x].left;
for ( int i = 0 ; i < VN_set[x].right.size() ; i++ )
{
string& str = VN_set[x].right[i];
int n = str.length() -1;
if ( isupper(str[n] ) )
{
int y = VN_dic[str.substr(n,1)]-1;
if ( str.length() > 1 && !isupper(str[n-1]) )
last[x].insert ( str[1] );
dfs1 ( y );
set<char>::iterator it = last[y].begin();
for ( ; it != last[y].end() ; it++ )
last[x].insert ( *it );
}
else
last[x].insert ( str[n] );
}
}
void make_last ( )
{
memset ( vis, 0, sizeof ( vis ) );
for ( int i = 0 ; i < VN_set.size() ; i++ )
if ( vis[i] ) continue;
else dfs1 ( i );
#define DEBUG
#ifdef DEBUG
puts("--------------LASTVT集---------------------");
for ( int i = 0 ; i < VN_set.size() ; i++ )
{
printf ( "%s : ", VN_set[i].left.c_str() );
set<char>::iterator it = last[i].begin();
for ( ; it!= last[i].end() ; it++ )
printf ( "%c ", *it );
puts ("" );
}
#endif
}
void make_table ( )
{
for ( int i = 0 ; i < MAX ; i++ )
for ( int j = 0 ; j < MAX ; j++ )
relation[i][j] = ' ';
for ( int i = 0 ; i < VN_set.size() ; i++ )
for ( int j = 0 ; j < VN_set[i].right.size() ; j++ )
{
string& str = VN_set[i].right[j];
for ( int k = 0 ; k < str.length()-1 ; k++ )
{
if ( !isupper(str[k]) && !isupper(str[k+1]) )
relation[str[k]][str[k+1]] = '=';
if ( !isupper(str[k]) && isupper(str[k+1]) )
{
int x = VN_dic[str.substr(k+1,1)]-1;
set<char>::iterator it = first[x].begin();
for ( ; it != first[x].end() ; it++ )
relation[str[k]][*it] = '<';
}
if ( isupper(str[k]) && !isupper(str[k+1]) )
{
int x = VN_dic[str.substr(k,1)]-1;
set<char>::iterator it = last[x].begin();
for ( ; it != last[x].end() ; it++ )
relation[*it][str[k+1]] = '>';
}
if ( k > str.length()-2 ) continue;
if ( !isupper(str[k]) && !isupper(str[k+2]) && isupper(str[k+1]) )
relation[str[k]][str[k+2]] = '=';
}
}
#define DEBUG
#ifdef DEBUG
for ( int i = 0 ; i < VT.size()*5 ; i++ )
printf ("-");
printf ( "算符优先关系表" );
for ( int i = 0 ; i < VT.size()*5 ; i++ )
printf ( "-" );
puts("");
printf ( "|%8s|", "" );
for ( int i = 0 ; i < VT.size() ; i++ )
printf ( "%5c%5s", VT[i], "|" );
puts ("");
for ( int i = 0 ; i < (VT.size()+1)*10 ; i++ )
printf ("-");
puts("");
for ( int i = 0 ; i < VT.size() ; i++ )
{
printf ( "|%4c%5s", VT[i], "|");
for ( int j = 0 ; j < VT.size() ; j++ )
printf ( "%5c%5s", relation[VT[i]][VT[j]], "|" );
puts ("");
for ( int i = 0 ; i < (VT.size()+1)*10 ; i++ )
printf ("-");
puts("");
}
#endif
}
int main ( )
{
int n;
char s[MAX];
while ( ~scanf ( "%d", &n ) )
{
memset ( used, 0, sizeof ( used ) );
for ( int i = 0 ; i < n ; i++ )
{
scanf ( "%s", s );
int len = strlen(s),j;
for ( j = 0 ; j < len ; j++ )
if ( s[j] == '-' )
break;
s[j] = 0;
if ( !VN_dic[s] )
{
VN_set.push_back ( WF(s) );
VN_dic[s] = VN_set.size();
}
int x = VN_dic[s]-1;
VN_set[x].insert ( s+j+2 );
for ( int k = 0 ; k < j; k++ )
if ( !isupper(s[k] ) )
{
if ( used[s[k]] ) continue;
used[s[k]] = 1;
VT.push_back ( s[k] );
}
for ( int k = j+2 ; k < len; k++ )
if ( !isupper(s[k] ) )
{
if ( used[s[k]] ) continue;
VT.push_back ( s[k] );
used[s[k]] = VT.size();
}
}
#define DEBUG
#ifdef DEBUG
puts ("************VT集*******************");
for ( int i = 0 ; i < VT.size() ; i++ )
printf ( "%c ", VT[i] );
puts ("");
puts("*************产生式*****************");
for ( int i = 0 ; i < VN_set.size() ; i++ )
VN_set[i].print();
puts("************************************");
#endif
make_first();
make_last();
make_table();
}
}